/*
 * @(#)NOfFunction.java
 *
 * Copyright 2003-2005 Sun Microsystems, Inc. All Rights Reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *   1. Redistribution of source code must retain the above copyright notice,
 *      this list of conditions and the following disclaimer.
 * 
 *   2. Redistribution in binary form must reproduce the above copyright
 *      notice, this list of conditions and the following disclaimer in the
 *      documentation and/or other materials provided with the distribution.
 *
 * Neither the name of Sun Microsystems, Inc. or the names of contributors may
 * be used to endorse or promote products derived from this software without
 * specific prior written permission.
 * 
 * This software is provided "AS IS," without a warranty of any kind. ALL
 * EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING
 * ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
 * OR NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN MICROSYSTEMS, INC. ("SUN")
 * AND ITS LICENSORS SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY LICENSEE
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package org.wso2.balana.cond;

import org.wso2.balana.ctx.EvaluationCtx;

import org.wso2.balana.attr.BooleanAttribute;
import org.wso2.balana.attr.IntegerAttribute;

import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set;

/**
 * A class that implements the n-of function. It requires at least one argument.
 * The first argument must be an integer and the rest of the arguments must be
 * booleans. If the number of boolean arguments that evaluate to true is at
 * least the value of the first argument, the function returns true. Otherwise,
 * it returns false (or indeterminate, as described in the next paragraph.
 * <p>
 * This function evaluates the arguments one at a time, starting with the first
 * one. As soon as the result of the function can be determined, evaluation
 * stops and that result is returned. During this process, if any argument
 * evaluates to indeterminate, an indeterminate result is returned.
 * 
 * @since 1.0
 * @author Steve Hanne
 * @author Seth Proctor
 */
public class NOfFunction extends FunctionBase {

	/**
	 * Standard identifier for the n-of function.
	 */
	public static final String NAME_N_OF = FUNCTION_NS + "n-of";

	/**
	 * Creates a new <code>NOfFunction</code> object.
	 * 
	 * @param functionName
	 *            the standard XACML name of the function to be handled by this
	 *            object, including the full namespace
	 * 
	 * @throws IllegalArgumentException
	 *             if the function is unknown
	 */
	public NOfFunction(String functionName) {
		super(NAME_N_OF, 0, BooleanAttribute.identifier, false);

		if (!functionName.equals(NAME_N_OF))
			throw new IllegalArgumentException("unknown nOf function: "
					+ functionName);
	}

	/**
	 * Returns a <code>Set</code> containing all the function identifiers
	 * supported by this class.
	 * 
	 * @return a <code>Set</code> of <code>String</code>s
	 */
	public static Set getSupportedIdentifiers() {
		Set set = new HashSet();

		set.add(NAME_N_OF);

		return set;
	}

	/**
	 * Evaluate the function, using the specified parameters.
	 * 
	 * @param inputs
	 *            a <code>List</code> of <code>Evaluatable</code> objects
	 *            representing the arguments passed to the function
	 * @param context
	 *            an <code>EvaluationCtx</code> so that the
	 *            <code>Evaluatable</code> objects can be evaluated
	 * @return an <code>EvaluationResult</code> representing the function's
	 *         result
	 */
	public EvaluationResult evaluate(List inputs, EvaluationCtx context) {

		// Evaluate the arguments one by one. As soon as we can return
		// a result, do so. Return Indeterminate if any argument
		// evaluated is indeterminate.
		Iterator it = inputs.iterator();
		Evaluatable eval = (Evaluatable) (it.next());

		// Evaluate the first argument
		EvaluationResult result = eval.evaluate(context);
		if (result.indeterminate())
			return result;

		// if there were no problems, we know 'n'
		long n = ((IntegerAttribute) (result.getAttributeValue())).getValue();

		// If the number of trues needed is less than zero, report an error.
		if (n < 0)
			return makeProcessingError("First argument to " + getFunctionName()
					+ " cannot be negative.");

		// If the number of trues needed is zero, return true.
		if (n == 0)
			return EvaluationResult.getTrueInstance();

		// make sure it's possible to find n true values
		long remainingArgs = inputs.size() - 1;
		if (n > remainingArgs)
			return makeProcessingError("not enough arguments to n-of to "
					+ "find " + n + " true values");

		// loop through the inputs, trying to find at least n trues
		while (remainingArgs >= n) {
			eval = (Evaluatable) (it.next());

			// evaluate the next argument
			result = eval.evaluate(context);
			if (result.indeterminate())
				return result;

			// get the next value, and see if it's true
			if (((BooleanAttribute) (result.getAttributeValue())).getValue()) {
				// we're one closer to our goal...see if we met it
				if (--n == 0)
					return EvaluationResult.getTrueInstance();
			}

			// we're still looking, but we've got one fewer arguments
			remainingArgs--;
		}

		// if we got here then we didn't meet our quota
		return EvaluationResult.getFalseInstance();
	}

	/**
     *
     */
	public void checkInputs(List inputs) throws IllegalArgumentException {
		// check that none of the inputs is a bag
		Object[] list = inputs.toArray();
		for (int i = 0; i < list.length; i++)
			if (((Evaluatable) (list[i])).returnsBag())
				throw new IllegalArgumentException("n-of can't use bags");

		// if we got here then there were no bags, so ask the other check
		// method to finish the checking
		checkInputsNoBag(inputs);
	}

	/**
     *
     */
	public void checkInputsNoBag(List inputs) throws IllegalArgumentException {
		Object[] list = inputs.toArray();

		// check that there is at least one arg
		if (list.length == 0)
			throw new IllegalArgumentException("n-of requires an argument");

		// check that the first element is an Integer
		Evaluatable eval = (Evaluatable) (list[0]);
		if (!eval.getType().toString().equals(IntegerAttribute.identifier))
			throw new IllegalArgumentException("first argument to n-of must"
					+ " be an integer");

		// now check that the rest of the args are booleans
		for (int i = 1; i < list.length; i++) {
			if (!((Evaluatable) (list[i])).getType().toString()
					.equals(BooleanAttribute.identifier))
				throw new IllegalArgumentException("invalid parameter in n-of"
						+ ": expected boolean");
		}
	}

}
